This invention relates to an apparatus for producing spirally formed pipe, particularly spiral pipes having a diameter of approximately one inch or less.
There are several known ways to form a pipe by spirally or helically winding a continuous strip of metal, and joining adjacent edges of the wound strip to form a spiral lockseam in the pipe One such pipe forming machine is disclosed in my U.S. Pat. No. 4,567,742, issued Feb. 4, 1986. In that machine, a strip of metal is curled inside of a forming head to form a spiral cylinder. A clinching roller comes up through a bottom opening in the forming head and cooperates with a support roller inside the forming head to form the lockseam.
Other types of spiral pipe producing machines are disclosed in U.S. Pat. No. 3,132,616 (Hale), U.S. Pat. No 3,606,779 (Parma), Canadian Patent No. 927,212 and U.K. Patent No. 830 504. The pipes made with these machines are generally used for ventilation and fluid transport. The smallest diameter pipes that are typically made with these machines are a few inches in diameter. These patents do not generally discuss a lower limit on pipe diameter, but there are certainly lower limits because as the pipe diameter decreases, the friction in the forming head or mandrel increases to the point where it is too difficult to move the pipe further.
U S. Pat. No. 3,940,962 (Davis) discloses another type of spiral pipe producing machine, and represents that the disclosed machine can be used to make 1 to 36 inch diameter pipe In practice, however, it would be difficult to accurately produce one inch diameter pipe with the Davis machine because of the roller configuration that it uses to spirally form the pipe. Moreover, it would be difficult to fit both the semi-cylindrical mandrel 67 and anvil roller 47 inside of one inch diameter pipe in accordance with the Davis disclosure.
A large potential for small diameter spiral pipes exists in the filter market, such as automobile oil filters. These filters typically have a perforated inner metal cylinder that is approximately one inch in diameter. In the past, spiral pipes have not been used for these inner filter cylinders because conventional spiral pipe forming machines have not been capable of producing pipe one inch in diameter
Hence, for a long time filter pipes have been made in the following, inefficient manner. A metal blank is cut to the precise size needed for the final cylinder. The metal is perforated either before or after the blanking operation. The perforated blank is rolled into a cylinder, and sealed along a longitudinal seam. To prevent the cylinder from collapsing under pressure, the cylinder is corrugated, or a spring is inserted into the cylinder.
The disadvantages of making longitudinal filter pipe in this conventional manner are manifest. Because of various steps involved, continuous pipe production is difficult. Moreover, a different size blank must be used for every change in the diameter and length of the pipe.